Bluetooth: Prevent buffer overflow in l2cap config request

A remote user can provide a small value for the command size field in
the command header of an l2cap configuration request, resulting in an
integer underflow when subtracting the size of the configuration request
header.  This results in copying a very large amount of data via
memcpy() and destroying the kernel heap.  Check for underflow.

Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 56fdd9162da929fcacd0b31cd5e537c71a421c4b..7d8a66b04f50c5d63a6a8a9b2ba0e9e74dd591ec 100644 (file)
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -2334,7 +2334,7 @@ static inline int l2cap_config_req(struct l2cap_conn *conn, struct l2cap_cmd_hdr
 
        /* Reject if config buffer is too small. */
        len = cmd_len - sizeof(*req);
-       if (chan->conf_len + len > sizeof(chan->conf_req)) {
+       if (len < 0 || chan->conf_len + len > sizeof(chan->conf_req)) {
                l2cap_send_cmd(conn, cmd->ident, L2CAP_CONF_RSP,
                                l2cap_build_conf_rsp(chan, rsp,
                                        L2CAP_CONF_REJECT, flags), rsp);